That's the intention but unless they brought all their family over they'd probably find a need to leave at some point. So preventing re-entry is a plausible cause.
> obviously won't do much for terrorism prevention, because those people tend to leave the country contemporaneously with leaving the earth.
Unless their plot fails and they are trying to escape and regroup. Now how many of those failed plots that we were about to catch them but they escaped have we solved recently. I can't think of any.
Working with the government for a bit, I would say when stuff like this comes about, the reasons are usually more more about money. Something like a a company lobbied to get a large hundred million dollar contract to implement this. And it just happens that the head of DHS is first cousin with the CEO of said company.
